The advent of digital cinema has created new standards for cinema sound, such as the incorporation of multiple channels of audio to allow for greater creativity for content creators and a more enveloping and realistic auditory experience for audiences. Model-based audio descriptions have been developed to extend beyond traditional speaker feeds and channel-based audio as a means for distributing spatial audio content and rendering in different playback configurations. The playback of sound in true three-dimensional (3D) or virtual 3D environments has become an area of increased research and development. The spatial presentation of sound utilizes audio objects, which are audio signals with associated parametric source descriptions of apparent source position (e.g., 3D coordinates), apparent source width, and other parameters. Object-based audio may be used for many multimedia applications, such as digital movies, video games, simulators, and is of particular importance in a home environment where the number of speakers and their placement is generally limited or constrained by the confines of a relatively small listening environment.
Various technologies have been developed to more accurately capture and reproduce the creator's artistic intent for a sound track in both full cinema environments and smaller scale home environments. A next generation spatial audio (also referred to as “adaptive audio”) format has been developed that comprises a mix of audio objects and traditional channel-based speaker feeds along with positional metadata for the audio objects. In a spatial audio decoder, the channels are sent directly to their associated speakers or down-mixed to an existing speaker set, and audio objects are rendered by the decoder in a flexible manner. The parametric source description associated with each object, such as a positional trajectory in 3D space, is taken as an input along with the number and position of speakers connected to the decoder. The renderer utilizes certain algorithms to distribute the audio associated with each object across the attached set of speakers. The authored spatial intent of each object is thus optimally presented over the specific speaker configuration that is present in the listening environment.
Current spatial audio systems have generally been developed for cinema use, and thus involve deployment in large rooms and the use of relatively expensive equipment, including arrays of multiple speakers distributed around a theatre. An increasing amount of advanced audio content, however, is being made available for playback in the home environment through streaming technology and advanced media technology, such as Blu-ray disks, and so on. In addition, emerging technologies such as 3D television and advanced computer games and simulators are encouraging the use of relatively sophisticated equipment, such as large-screen monitors, surround-sound receivers and speaker arrays in home and other listening environments. In spite of the availability of such content, equipment cost, installation complexity, and room size remain realistic constraints that prevent the full exploitation of spatial audio in most home environments. For example, advanced object-based audio systems typically employ overhead or height speakers to playback sound that is intended to originate above a listener's head. In many cases, and especially in the home environment, such height speakers may not be available. In this case, the height information is lost if such sound objects are played only through floor or wall-mounted speakers.
To overcome issues with height speakers along ceilings or upper walls, reflected sound speakers have been developed to allow floor or low mounted speakers to reflect audio content with height cues off of the ceiling or upper walls. Such as product and system is described in patent application No. 62/007,354, which is hereby incorporated by reference in its entirety. FIG. 1 illustrates the orientation of an upward firing speaker as so described. As shown in FIG. 1, a floor or bookshelf speaker 102 includes a driver or driver array oriented upwards to reflect sound off a point or area 104 on an upper surface, typically the ceiling, onto the listening position 106 so that sounds intended to originate from the height location still do so even if they are projected from a much lower location 102. This effectively replaces a height or ceiling loudspeaker with a more convenient floor standing unit.
As is known, a loudspeaker driver is a device that converts electrical energy into acoustic energy or sound waves. In its simplest form, a typical loudspeaker driver consists of a coil of wire bonded to a cone or diaphragm and suspended such that the coil is in a magnetic field and such that the coil and cone or diaphragm can move or vibrate perpendicular to the magnetic field. An electrical audio signal is applied to the coil and the suspended components vibrate proportionally and generate sound. With respect to speaker dispersion, a traditional loudspeaker driver, mounted in a cabinet has a dispersion or directivity character which is wide, often omnidirectional, at low frequencies and narrow, or more directional, at higher frequencies. FIG. 2 shows example a cross section view of a loudspeaker cone 204 in a sealed cabinet 206 and how the sound radiation pattern or dispersion becomes narrower at higher frequencies. As shown in FIG. 2, the sound dispersion pattern 201 at low frequencies is very wide, substantially 360 degrees for the example shown, while the sound dispersion pattern 203 for mid-frequencies is narrower (e.g., 120 degrees), while the sound dispersion pattern 205 for high frequencies is narrower still (e.g., 60 degrees). The amount of narrowness also depends on the size of the loudspeaker driver, with larger diameter drivers exhibiting narrower dispersion at lower frequencies than smaller diameter drivers.
When a typical circular cone loudspeaker driver is used in an upward firing loudspeaker, as in FIG. 1, lower frequency sounds radiate in all directions whilst higher frequency sounds radiate toward the ceiling and reflect off the ceiling to toward the listening position, in accordance with the frequency-dependent sound dispersion patterns shown in FIG. 2. FIG. 3A illustrates an example high frequency sound dispersion pattern 302 for a typical known upward firing loudspeaker firing reflected sound off of a ceiling. FIG. 3A shows the effect of the higher frequency dispersion pattern for a typical loudspeaker driver used to reflect sound of a ceiling. As shown in FIG. 3A, a fairly narrow angle of radiation 301 from the driver becomes a fairly wide area 303, once the sound has reflected from the ceiling and down onto listening position 307.
For typical stereo or surround sound audio content, speakers are often deployed in pairs. Thus, the speaker array in FIG. 3A may actually comprise two upward firing speakers placed on either side of the television or viewing screen. FIG. 3B shows a front view of the sound dispersion for the speaker setup of FIG. 3A. As shown in FIG. 3B, the two (left and right) upward firing loudspeakers create respective reflected sound dispersion patterns 304 and 306, which provide separate left and right ceiling sound images. FIG. 3C shows a top view of the sound dispersion patterns of FIG. 3B. It can be seen in FIGS. 3B and 3C that at high frequencies, neither speaker provides good sound coverage at the listening position. A person sitting in the center receives little energy from both speakers, and person sitting at either side of the listening position 307 received predominantly energy from the nearest upward firing loudspeaker. One way to provide more even high frequency coverage at the listening position 307 is to rotate the loudspeakers such that they face the listening position. This is shown in FIGS. 4A and 4B, where FIG. 4A illustrates a front view of example sound dispersion for the speakers of FIG. 3A rotated inwards and FIG. 4B illustrates a top view of the sound dispersion patterns 404 and 406 of FIG. 3B. As can be seen in FIGS. 4A and 4B, the overlapping region 403 of the high frequency sound is not large and is very dependent on loudspeaker aiming, as shown for the example rotation angle 402 for the loudspeakers, which helps overlap the two sound dispersion patterns 404 and 407 onto listening position 407.
What is needed therefore, is a speaker system for reflected sound that provides wider horizontal or side-to-side dispersion to better cover the listening area.
For purposes of the present description, the term loudspeaker means complete loudspeaker cabinet incorporating one or more loudspeaker drivers; a driver or loudspeaker driver means a transducer which converts electrical energy into sound or acoustic energy, and sound dispersion or dispersion means or describes the directional way sound from a source, in this case a loudspeaker, is dispersed or projected. Wide dispersion indicates that a source radiates sound widely and fairly consistently in many directions; the widest being omnidirectional where sound radiates in all directions. Narrow dispersion indicates that a source radiates sound more in one direction and over a limited angle. Dispersion can be different in different axes, for example vertical and horizontal, and can be different at difference frequencies.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions. Dolby and Atmos are registered trademarks of Dolby Laboratories Licensing Corporation.